1. Field of the Invention
The present invention relates to a seatbelt apparatus for a vehicle that restrains an occupant in a seat by a webbing.
2. Description of the Related Art
A known seatbelt apparatus for a vehicle has an emergency locking retractor that mechanically locks a webbing so as not to be pulled out when the vehicle is in emergent circumstances in which the behavior of the vehicle is unstable.
In the emergency lock mechanism, a lateral face of a belt reel, around which a webbing is wound, is provided with a locking activation drum that rotates relative to a belt reel when a torque greater than or equal to a predetermined amount is acted between the locking activation drum and the belt reel; and a locking claw that meshes with a lock groove of a casing when the belt reel rotates relative to the locking activation drum in a predetermined direction. In addition, the emergency lock mechanism, at a position closer to the locking activation drum, is provided with an emergency operation unit that is activated when the vehicle is in an unstable state (e.g., when acceleration greater than or equal to a predetermined amount acts on the vehicle or the vehicle inclines at an angle greater than or equal to a predetermined amount). The activation of the emergency operation unit thereby gives a braking power to the locking activation drum.
For this reason, the activation of the emergency operation unit due to such unstable behavior of the vehicle brakes the locking activation drum, and the belt reel rotates relative to the locking activation drum in a first direction when the webbing is just about to be pulled out. The rotation makes the locking claw mesh with the lock groove, and thereby locking the belt reel so as not to rotate in the webbing unwinding direction.
Further, if the belt reel starts rotating in the webbing winding direction due to a force from a return spring, in which the belt reel loses a driving force in the webbing unwinding direction because of the activation of the emergency locking retractor, the mesh between the locking claw and the lock groove is automatically released after a predetermined amount of rotation of the belt reel relative to the locking activation drum in a second direction.
Incidentally, there has been known a seatbelt apparatus in which a driving motor is connected to a belt reel in order to help a return spring to wind a webbing and to restrain an occupant in response to a state of a vehicle (refer, for example, to Japanese Unexamined Patent Application, First Publication No. 2008-105552).
In the seatbelt apparatus having a driving motor described above, the driving motor is driven if a buckle of a seatbelt is pulled out or a change of a vehicle state is detected. Therefore, the driving motor is not directly involved in unlocking the emergency locking retractor of which the operation is mechanically independent. Normally, the unlocking of the emergency locking retractor is performed by a force from a return spring when the vehicle recovers from an unstable state. However, it is difficult to perform an automatic unlocking in the following circumstances (1) and (2).
(1) There is no substantial margin for winding the webbing when the webbing is rapidly or gradually wound up by the return spring during large fluctuations of the upper body of an occupant in which the emergency locking retractor is activated due to abrupt acceleration of the vehicle or traveling of the vehicle on a rough road.
Specifically, the case is, even when the vehicle recovers from an unstable state, the automatic unlocking by the return spring is impossible because the reaction force from the tightly fastened occupant is large.
In this case, since the automatic unlocking of the webbing does not work, the occupant has to pull the buckle out.
(2) An upper body of an occupant receives slowly moves due to a weak centrifugal force or the occupant intentionally tries to move the upper body, after the emergency locking retractor is activated when the vehicle travels in a curve or takes a corner at a speed greater than or equal to a predetermined amount.
In this case, the occupant would more comfortably drive if the restraint by the webbing does not work, but actually an unnecessary restraint force acts on the occupant. That causes the occupant discomfort and makes it difficult for the occupant to handle the vehicle.
In view of the circumstances described above, the present invention has an object of providing a seatbelt apparatus for a vehicle that is capable of enhancing comfort and handling of the vehicle in which unnecessary locking, that is continuously effective after an activation of a emergency locking retractor, is released.